(1) Field of the Invention
This invention relates to a corrosion inhibiting composition for use in commercial, institutional, and industrial water systems. The compositions comprise a mixture of (1) a fatty acid ester, and (2) a polyalkylene glycol, preferably polyethylene glycol. These compositions are useful in inhibiting the corrosion of metals such as steel, copper, and brass, which are exposed to water.
(2) Description of the Related Art
The pipes, heat exchangers, equipment, and other components of commercial, institutional and industrial water systems, are often made of metal such as steel, copper, and brass, which corrode after time when subjected to oxygen, moisture, and corrosive gases. Examples of such industrial systems include cooling water systems, boiler systems, including steam condensate, heat transfer systems, refinery systems, pulp and paper making systems, food and beverage systems, and mechanical coolant systems. Examples of institutional and commercial systems include HVAC systems, sterilizers, and kitchen steam tables.
Corrosion of metallic components in these systems can cause system failures and shutdowns. In addition, corrosion products accumulated on the metal surface decreases the rate of heat transfer between the metal surface and the heat transfer medium, such as water, which reduces the efficiency of the system.
In order to inhibit corrosion of the metal surfaces in these systems, especially of steam condensate return lines, volatile amines, filming amines, or amine derivatives are added to water and steam in such systems, e.g. to the feedwater or other injection points used for this purpose. However, amines may have limitations from an environmental or toxicity standpoint, especially in humidification and food contact.
U.S. Pat. No. 5,849,220 discloses the use of non-amine filming inhibitors, which are a combination of a surfactants comprising (1) at least one sorbitan fatty acid ester surfactant, and (2) at least one polyoxyethylene derivative of a sorbitan fatty acid ester. These non-amine inhibitors have environmental benefits because they are less toxic, more biodegradeable, and can be used in many products made for human consumption, because they have a less objectionable odor and taste.
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This invention relates to a corrosion inhibiting composition for use in inhibiting the corrosion of metallic surfaces exposed to water comprising a mixture of:
(1) a fatty acid ester, and
(2) a polyalkylene glycol.
These compositions are useful in inhibiting the corrosion of metals such as steel, copper, and brass, which are exposed to water or other industrial fluids.
The examples herein illustrate that the combination reduces corrosion in steel, copper, and other metallic surfaces, and that this result is unexpected, or synergistic, in view of the limited inhibition effect of the components alone. In addition to the environmental advantages of the corrosion inhibiting compositions described in U.S. Pat. No. 5,849,220, which contains a polyoxyethylene derivative of a sorbitan fatty acid ester instead of a polyalkylene glycol, the compositions of the subject invention provide improved corrosion resistance when compared to the corrosion inhibiting compositions described in U.S. Pat. No. 5,849,220.
The invention also relates to a method of reducing corrosion on metallic surfaces exposed to water in an industrial, commercial or institutional system, which comprises adding a corrosion inhibiting amount of the composition to the water or steam at an injection point, such that the corrosion inhibiting composition comes into contact with the metal surface.
Examples of such commercial, institutional and industrial systems, which contain metallic components exposed to water, include, for example, cooling water systems, boiler systems, heat transfer systems, refinery systems, pulp and paper making systems, food and beverage systems, mechanical coolant systems, water treatment systems, refinery and oil field processes, metal making, mining and ore processing applications, beverage production, hospital sanitation systems, and pharmaceutical manufacturing.
The corrosion-inhibiting composition is effective over a broad pH range, especially under slightly acidic solutions, preferably between a pH of 5 to 9, more preferably from about 5 to about 7, and most preferably from about 5.5 to about 7. The temperature of the industrial fluid typically ranges from about 10xc2x0 C. to about 250xc2x0 C., more typically from about 15xc2x0 C. to about 95xc2x0 C. The corrosion inhibiting composition is injected directly into the vapor phase, liquid phase, or both phases of the industrial system.
The detailed description and examples will illustrate specific embodiments of the invention will enable one skilled in the art to practice the invention, including the best mode. It is contemplated that many equivalent embodiments of the invention will be operable besides these specifically disclosed. All units are in the metric system and all percentages are percentages by weight unless otherwise specified.
Although other fatty acid esters are useful in formulating the corrosion inhibiting compositions, preferably the fatty acid ester is a sorbitan ester of a saturated fatty acid having from 16 to 18 carbon atoms. Most preferably, the sorbitan fatty acid ester is selected from the group consisting of sorbitan monostearate, sorbitan monopalmitate, sorbitan monooleate, sorbitan sesquioleate, and mixtures thereof. Examples of suitable sorbitan fatty acid esters are sold under the following trademarks: SPAN 60 and ARLACEL 60 (sorbitan monostearate), SPAN 40 and ARLACEL 40 (sorbitan monopalmitate), SPAN 80 and ARLACEL 80 (sorbitan monooleate), and ARLACEL C and ARLACEL 83 (sorbitan sesquioleate).
Particularly useful as the polyalkylene glycol in formulating the corrosion inhibiting composition are polyethylene glycol, polypropylene glycol, and mixtures thereof, most preferably polyethylene glycol. The polyethylene glycols that are useful in formulating the corrosion inhibiting compositions are prepared according to well known methods, and have an average molecular weight of 200 to 1000, more preferably from about 300 to 600, most preferably about 400. Examples of commercially available polyethylene glycols include the CARBOWAX SENTRY line of polyethylene glycols from Dow Chemical.
The weight ratio of the fatty ester to polyalkylene glycol is typically from about 1:1 to 10:1, preferably from about 2:1 to about 5:1 more preferably about 5:1.
The dosage of the corrosion inhibiting composition typically ranges from about 1 ppm to about 200 ppm, preferably from 1 ppm to 60 ppm. In steam and steam condensate treatment we will use 1 to 3 ppm. based upon the amount of active components (1) and (2) in the corrosion inhibiting composition.
The compositions may contain one or more optional components, for instance thickeners and preservatives.
The following abbreviations are used:
PEG polyethylene glycol sold under the trade name CARBOWAX SENTRY POLYETHYLENE GLYCOL NF by Dow Chemical
SME sorbitan monoester of stearic acid, sold by ICI under the trade name SPAN 60.
PAG-SME oxyethylene adduct of SME prepared by reacting about 20 moles of ethylene oxide with SME, sold under the trade name TWEEN 60, which is used in the corrosion inhibiting compositions of U.S. Pat. No. 5,849,220.